Uniform spraying apparatus



Nov. 1, 1966 Filed June 22, 1964 O. B. JOHNSTON ET AL UNIFORM SPRAYINGAPPARATUS 3 Sheets-Sheet 1 NOV. 1, 1966 Q B JOHNSTON ET AL 3,282,273

UNIFORM SPRAYING APPARATUS Filed June 22, 1964 5 Sheets-Sheet 2 "MN/M 01w W p x x I a! NOV. 1, 1966 Q. JOHNSTON ET AL 3,282,273

UNIFORM SPRAYING APPARATUS 5 Sheets-Sheet 5 Filed June 22, 1964 A 4&2

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wQ MA/r may/r I i/ W MM/7 if United States Patent 3,282,273 UNIFORMSPRAYING APPARATUS Orin B. Johnston, 7428 Lyndale Ave. 5., Minneapolis,Mind, and Charles M. Sheldon, 9404 E. Bush Lake Road, Bloomington, Minn.

Filed June 22, 1964, Ser. No. 376,632 Claims. (Cl. 134-102) Thisinvention relates to improved apparatus for the spraying of liquids, sothat an accurately uniform coating or film of a liquid may be applied toa comparatively large target area or workpiece surface. One particularuse of the apparatus of this invention is in the application of etchantto the surfaces of workpieces, and equipment for this particular purposewill be shown and described herein by way of one example. However, inits broader aspects the present invention is not limited to etching, butmay be used in applying thin films to sheets or surfaces, in spreadingprotective or decorative coatings, in washing, or in fact in almost anyprocess where the uniform and controlled spraying of liquid over anextended surface or area is essential.

The general object of this invention therefore is to provide a means forthe spraying of liquids in a uniform manner over relatively extendedareas. Another object of this invention is to provide such spraying witha degree of control such that improved technical results are obtained inthe workpieces or objects being sprayed, as in chemical etching. Afurther object is to provide such a spraying apparatus that substantialeconomies may be made in the amount and character of liquid used in thespraying.

Still further objects and advantages of this invention will becomeapparent from the following general and detailed description and theclaims, taken with the accompanying drawings in which are illustratedbasic arrangements and one example of spraying equipment embodying thepresent invention and incorporating improvements for obtaining theobjects set forth above.

In the drawings:

FIG. 1 is a diagrammatic transverse vertical sectional view of anarrangement of basic elements in spraying equipment according to thisinvention;

FIG. 2 is a corresponding side vertical sectional view of thearrangement of the elements of FIG. 1;

FIG. 3 is a similar side vertical sectional view of a modifiedarrangement of basic elements in spraying equipment according to thisinvention;

FIG. 4 is a perspective view of apparatus showing the genenal layout andsome details of an installation of spraying equipment according to thepresent invention, designed for a particular purpose hereinafterdescribed;

FIG. 5 is a vertical sectional view through the spraying chamber in theapparatus of FIG. 4 with associated mechanisms, showing how thearrangement of basic elements in FIG. 1 is applied in this particularinstallation;

FIG. 6 is a vertical sectional view through the spraying chamber in theapparatus of FIG. 4, at right angles to the section of FIG. 4, andcorresponds to the arrangement of basic elements shown in FIG. 2;

FIG. 7 is a horizontal section on the line 77 of FIG. 6 on a reducedscale showing a mechanism for feeding work to the spraying areaaccording to the invention and applicable to the particular installationshown in FIG. 4;

FIG. 8 is a schematic view showing the air flow or pneumatic system ofthe particular installation of FIG. 4, and

FIG. 9 is a schematic view or diagram showing a temperature controlsystem for the apparatus of FIG. 4 and its relation to the air flowsystem of FIG. 8.

The basic elements of equipment according to this in- 3,282,273 PatentedNov. 1, 1966 vention include a liquid spraying means 10, a meanssupplying pneumatic propellent medium 20, a work holder 30, and anarrangement to cause a certain relative movement between the liquidspraying means and the work holder, this being partly included in thereciprocating mechanism 40 in the drawings. Also included as basicelements or arrangements may be an enclosure or chamber 50 for housingthe liquid spraying means, propellent medium supply and work holder anda collector 60 for disposing of spent or excess liquid and propellentmedium from within the enclosing chamber or housing. These referencenumerals will be used throughout the drawings to indicate generally theparts, portions, or assemblies comprising these basic elements.

In the diagrams of FIGS. 1, 2, and 3, the liquid spray means 10comprises a number of sprayheads 11 supplied by pipes or tubes 12 withliquid to be sprayed. For reasons that will later appear the feed ofliquid to the sprayheads is kept at a constant or uniform rate. Thepneumatic propellent medium may be air or other suitable gaseous mediumdepending upon the nature of the spraying to be done. For conveniencehereafter it will be described as air unless a different meaning isobvious from the context. In the diagrammatic figures the propellent airis supplied through a conduit 20 to shields 22 surrounding eachsprayhead 11. The pressure and flow of the air as well as that of theliquid is kept uniform. Although the sprayheads and pneumatic propellentarrangements illustrated herein are of the type shown and described inthe United States patent issued November 13, 1956, to Henri Coanda, No.2,770,501, they may be of other designs exhibiting characteristics ofconsistent performance in the uniform atomizing and spraying of liquidssupplied at uniform rates and using a flow of propellent gas underuni-form pressure. The Coand-a spraying apparatus has advantages in theexcellent atomization of liquids being sprayed and the fact thatrelatively low pressure propellent air may be used.

In selecting the spray means, it should be considered that thepropelling of liquid by air increases the energy by which dropletsimpinge on the work surface being sprayed. In etching apparatus ashereafter described, this greatly improves the etching reaction overthat obtained by spraying the liquid alone without propellent air. Also,because of the continued air pressure on liquid already sprayed on aworkpiece, pneumatic spraying will tend to spread any given amount ofliquid over a greater work surface area than would be covered withoutthe pneumatic propellant. These advantages mean that less liquid or lessactive liquid may be used in obtaining desired results on a work surfacewith an .air propelled or pneumatic spray than must be used to obtaincomparable results with liquid which moves from a source to the worksurface as a function of kinetic energy stored in or imparted to it.

The work holder 30 indicated in FIGS. 1 through 3 is an endless belt 3-1suitably guided and driven about a pair of rollers 32 to carry objectsor articles 33 at a uniform rate past the sprayheads 1-1 at a fixedspacing therefrom. Of course, in case of lengths of materials such asphotographic film the material to be sprayed may be selfsupporting whereis passes the sprayheads and in such an endless belt or similar carrierneed not be used. Obviously, the surface being sprayed can have anycontour as long as the desired fixed spacing from the spray means can bemaintained.

As can be readily understood, the spray pattern of a single sprayheadwhich is stationary over a stationary object will not be uniform. Thatis, each sprayhead will produce a pattern in which much of the liquidbeing sprayed is concentrated at some central point or focus and theconcentration decreases in all directions from the center. However, ifthe piece to be sprayed is moved in a given direction, greateruniformity of distribution will be obtained in the direction ofmovement, especially if the movement is kept at a uniform rate. If,however, the sprayhead is simultaneously moved in a direction at rightangles from the movement of the work, then most of the effects of lackof uniform distribution may be overcome. The relative motion between thework and the sprayhead can be achieved in various ways. Although it ispossible to move the article being sprayed in two axes at the same time,it is found to be simpler and just as effective to move the work in onedirection and to oscillate the sprayhead back and forth transversely tothe direction of work movement. The reciprocating means for thesprayhead assembly is shown as a suitably driven sliding shaft 42connected to the sprayhead assembly 10. Suitable guides are provided forthe sprayhead assembly to insure that the spacing between the sprayheadsand the workpieces or target area remains constant during thereciprocation or oscillation. The degree of uniformity of spraying willdepend upon the relative velocities of the work and the sprayer andtherefore for best results, both the speed of movement of the work andthe speed of oscillation or reciprocation of the sprayhead are adjustedand controlled to achieve the desired result.

Optimum results are obtained by a reciprocating motion in whichacceleration and deceleration at each end of the stroke are as rapid aspossible, with a minimum of pause, and the travel back and forth is keptat the same uniform rate. For example, in a machine having a spacingbetween centers of sprayheads of about two inches and a length of strokein each direction adjustable from a minimum of about one inch tosomething over two inches, depending upon the type of work beingperformed, the reciprocation may .take place at about 150 cycles perminute or five strokes back or forth every second, with no perceptiblepause at the end of each stroke, excepting that needed to stop themotion and rereverse direction. This order of reciprication could beused with a workpiece surface being traversed past the sprayheads atabout one inch per minute. The above rates of speed given are exemplaryonly and may be varied considerably to suit the requirements ofparticular spraying operations and to obtain the best results.

If the particular workpiece is massive or it is otherwise impractical orundesirable to move the workpiece, the sprayhead assembly alone may bemoved in both a first axis and a second axis at an angle to the firstaxis at the same time, to integrate or cancel out the localized sprayingeffect. The effect desired may be described as obtained by reciprocatingrelative movement between the workpiece or target area and the sprayheadassemly regularly and periodically back and forth in a first directionwhile at the same time causing relative movement between the work andthe sprayheads in a second direction substantially at right angles tothe first direction, all of this while maintaining a uniform fixeddistance between the sprayheads and the surface of the workpiece ortarget area.

For the sake of economy in the use of materials as well as to preventundesired reaction of the surrounding atmosphere on the work beingsprayed, the enclosure may be regarded as a basic element. Because bothliquid and air are being supplied through this encolsure during thespraying, provision should be made to dispose of or carry away excess orundesired liquid and air and for this purpose a collector 60, shown herein the form of a sump with an air discharge conduit 61 and a liquiddrain pipe 62, are provided in the bottim of the enclosing chamber. Ingeneric aspects of the invention, other collectors, such as suctionscavening arrangements, might be used to remove liquid and dispose ofthe air, these being positioned above or to the side of the surfacebeing sprayed and located to remove the liquid and air after the workhas moved beyond the spraying area.

FIG. 3 shows a modification of the basic arrangement shown in FIGS. 1and 2. In this form, there are in effect two compartments within theenclosure 50, compartment 51 holding a first set of sprayheads forspraying the work as it passes beneath, and compartment 52 holding asecond set of sprayheads. A dividing wall 53 separates the compartments.The work may be sprayed with a first substance or solution incompartment 51, for example, an etchant, and then the reaction instantlystopped or changed by spraying with a second substance or solution, forexample, a neutralizer from the sprayheads in compartment 52.. Thematerial discharged from the two sets of sprayheads may be collected ina common tank or drain from the sump and drain pipe 62, the liquidmaterial being handled or treated in any desired manner. If air locks orseals are provided where the conveyor 31 enters and leaves the enclosingchamber 50, the air discharge conduit 61 may handle the air supplied tothe spraying chamber and either discharge it to the atmosphere orrecirculate it for use in providing continued pneumatic propellantpressure through the conduit 20, as will be described hereafter inconnection with the illustrative example of etching equipment.

The basic method of spraying according to this invention should be clearfrom the above as inluding the requirements or steps of 1) maintaining afixed distance between the liquid spray means (sprayheads) and thesurface of a workpiece (2) providing a constant rate of flow of liquidto the sprayheads and a constant rate of flow of propellant gas toatomize and direct liquid from the spray means toward the workpiece (3)causing reciprocating relative movement between the spray means and theworkpiece regularly back and forth in a first direction andsimultaneously causing relative movement between said spray means andsaid workpiece in a second direction substantially at right angles tosaid first direction while maintaining the fixed distance between thespray means and the workpiece.

The basic arrangements and method described above, with certain noveladditions and refinements, are incorporated in the chemical etchingmachine of FIGS. 4 through 9 inclusive. In this particular machine abase cabinet 70 encloses and supports practically all of the necessaryequipment and controls. The cabinet in this exemplary illustration has ahorizontal table top or work surface 71 near one end of which is locatedthe spray chamber 59, most of which is located above the level of thework surface 71, but part of which, including the air and liquidcollector, is located inside the cabinet. The top of the spray enclosureis in the form of a plenum chamber 23 and a horizontal supporting wall54 supports the sprayhead assembly 13 and divides the enclosure toseparate the plenum chamber from the spraying area proper, 24. Thesprayheads 111, shown as of the Coanda type above-mentioned, aresuspended in an aligned array at uniform spacings lengthwise of theelongated carrier member 14 and each head has its own pair of supplypipes 12 for liquid being fed thereto. The supply pipes extend upwardlythrough the carrier member 1 and have flexible tubing 15 secured theretoleading outwardly of the enclosure 50 as through an opening 5 and to aliquid feeding and metering device of a character later described. Alsodepending from the carrier member 14 is an air shield 25 having passagesopening into the plenum chamber 23 and leading to individual openings 26around each sprayhead for the discharge of propellent air at eachsprayhead. The plenum chamber is supplied with air under a controlledand uniform pressure and velocity from a duct 27.

The carrier member 14- and therefore the entire sprayhead assembly iscaused to move in a reciprocating motion in guides 16 carried by thehorizontal wall 54. The reciprocating motion in this case may beobtained by movement of a piston in an air cylinder 43, the piston rod44 being secured to one end of the sliding carrier member 14 andprovided with appropriate means such as an alternating reversing limitswitch 45 to control the periodicity and extent of reciprocatingmovement of the piston in the air cylinder. Such arrangements forobtaining controlled reciprocating movement are varied and well knownand therefore need not be further described here. It is enough to saythat the lep gth of the reciprocating stroke and its frequency can beadjusted to meet the requirements of any specific job. The purpose ofthe reciprocating motion is to provide the integrating effect describedearlier, to eliminate any nonuniformity of spray patterns in an axisperpendicular to the direction of the travel of work. Assuming the workis traversed at a uniform rate in one axis, integration to eliminatespray pattern nonuniformities thus is provided for in both axes of thepart being sprayed.

Referring particularly to FIG. 7, the work holder in this form of theinvention is shown as a carriage 34 slidably carried in Ways 35 in thebottom of the chamber 50 at a level below that of the work surface 71 onthe base cabinet. This work carriage is moved from below a loadingopening 55 in the table top 71, through the spraying area 24 of thespraying chamber and to a position below an unloading opening 56 on theother side of the housing 50. The openings 55 and 56 may be closed in asealed fashion by suitable doors 57 operated by hand levers 58. Motionof the carriage 34 through the spraying area is controlled by an aircylinder 36, at times and at speeds governed by a hydraulic controlcylinder 37 and the wishes of the operator. Assuming that the carriageis empty and is in position under the loading opening 55, the door 57 isopened, the work is inserted onto the carriage, the door closed, and theair cylinder 36 is caused to be actuated by the operator at a selectedspeed controlled by the cylinder 37. The carriage will slide in the ways35 and reach a position under the unloading opening 56, at which timethe door above it may be opened and the work removed. The operator canthen reversely actuate the air cylinder to drive the carriage back toits original location. Arrangements and controls for driving the carrierare, like those for reciprocating the sprayhead carrier 14, of a natureso well known as not to require detailed description. The uniformcarriage movement integrates out any nonuniformity of the spray patternin the direction of travel of the carriage. The above-described drive isbut one arrangement that might be used. With other arrangements fordriving after unloading, the workpiece carrier may be reloaded at theunloading" station and then returned to its original position, withspraying also taking place during a controlled speed return movement. Insome cases there might be a single loading and unloading station and thecarriage could be moved back and forth into and out of the spray ingchamber, the workpieces being subjected to two passes at a controlledspeed under the sprayheads, or to a single pass, by cutting off thespray liquid when the carriage is being moved in one direction or theother.

Particularly advantageous results are obtained if the pneumaticpropellent medium is recirculated and its temperature is carefullycontrolled. FIG. 8 shows schematically a closed loop temperaturecontrolled system of this type used in the apparatus of FIG. 4. Thepneumatic system is powered by a blower 80. Air from the outlet of theblower passes through a duct 81 which may be located near the end of theplenum chamber duct 27 at or below table level. The parts of the airsystem so far described are not seen in FIG. 4 because they are locatedeither in back of or under the cabinet. From the duct 81 a duct 83 leadsto an air mixing chamber and valve 84. From this mixing chamber andvalve, depending upon the position of the valve setting, all or part ofthe air will flow through a duct 86 to and through a heat exchanger 87,into the duct 88, and again through a portion of the air mixing chamberand valve 84, from which it exits into a duct 89 leading to the plenumchamber supply duct 27. Depending upon the temperature control demandand therefore the position of the valve 85 in the air mixing chamber andvalve 84, all of the air may pass from duct 83 through the chamber andvalve and then exit into duct 89 without any of the air being routedthrough the heat exchanger 87. This is part of the temperature controllater described.

Air from the duct 27 flows into the plenum chamber 23 and through theopenings 26 in the sprayhead assembly to propel the liquid. After theair passes out of the sprayhead assembly and serves to atomize andpropel the liquid etchant against the work in the spraying area 24, itflows into the air discharge conduit 61. Entrained liquid is is carriedby this air and therefore, after going through the discharge conduit 61,it is passed through a filter chamber 63 which separates the entrainedliquid from the air. From the filter chamber 63 the cleaned air then ispassed as through a conduit 64 to the blower 80, completing the aircircuit.

With an entirely sealed, closed-loop pneumatic system, a gas can be usedthat is inert, chemically, to the liquid being sprayed, or to the workbeing processed, or both. Not only this, but by proper control of theinput and exhaust rate from the chamber. A chemically inert atmosbecreatted in the spraying chamber and maintained by keeping the gas inputat a rate not greater than the exhaust rate from the chamber. Achemically inert atmosphere is useful where the spraying might bedeleteriously affected by undesirable substances in ordinary air.Sub-atmospheric pressure in the spraying chamber will improve theatomization of the liquid being sprayed and the transfer of the atomizedliquid to the workpiece or target area.

Air friction and turbulence occurring principally in the blower andbecause of compression in parts of the air flow system, cause the airtemperature to rise. Three loops of temperature control have beenprovided in the exemplary apparatus to provide accurate control of airtemperature and of the etchant temperature to a preselected level set byt-he operator. The schematic coolant control diagram (FIG. 9), shows therefrigeration, heat exchangers, and temperature control of the coolantand refrigerant and relation to the heat exchanger 87 in the aircircuit.

The first control loop includes a refrigerant compressor 72 andrefrigerant-coolant heat exchanger 73 in the refrigerant circuit 74.Control of the temperature of this loop is obtained in the usual mannerby a sensor responsive to temperature in the heat exchanger 73,governing action of the compressor 72.

The second control loop includes the heat exchanger 73, common to therefrigerant circuit and to the coolant circuit 75, which may carry amixture of water and antifreeze as the cooling medium. A three-way valve76 driven by a control motor 77 in accordance with the demands of asensor 78 in the coolant circuit at a point sensitive to the temperaturein coolant-air heat exchanger 87, governs the mixture of the coolantcirculating in this loop, directing it either through the circulatingpump 79 and heat exchanger 73 or through the heat exchanger 87 as well.Circulation of coolant through the heat exchanger 87 is made only whencalled for by sensor 78.

The third control loop is the air circulation system, including the heatexchanger 87. This loop responds to a unit sensing the temperature forexample in the duct 27 leading to the plenum chamber. Other locations ofthis temperature sensing unit may be found desirable. Such sensing unitcommands the motor-driven butterfly valve in the air mixing chamber andvalve 84, as above described, directing all or part or none of the airfrom duct 86 through heat exchanger 87 before it reaches the plenumchamber supply duct 27.

In cases where it is desired that the liquid be applied at an elevatedtemperature, the heat exchanger 87 can befurnished with a heater,properly controlled to maintain the air temperature at a desired raisedlevel so that the liquid propelled at the sprayheads will be effectivelyraised to a corresponding temperature.

Temperature control systems of the kind or type desired may be varied atwill and are readily understood in the temperature control art. Ultimatecontrol of only the circulating air temperature is characteristic ofpreferred apparatus according to this invention. With properly designedsprayheads, the etchant or other liquid is atomized into extremely fineparticles. Finely atomized particles have an area to mass ratio of ahigh numerical value. Thus, the time required for the liquid to receivethermal energy from the propellent air is reduced to an infinitesimalamount. Consequently, the liquid temperature is accurately and readilycontrolled by controlling the temperature of the propellent air only.The temperature of the liquid being sprayed therefore can be controlledwith extreme accuracy and can be changed from one desired temperature toanother virtually instantaneously by resetting the air temperaturecontrol.

Since the liquid being atomized can have its temperature rapidly changedto the desired working temperature by the pneumatic propellant at thepoint of spraying, it 2 can be stored in the liquid supply vessel at atemperature most suitable to maintain its desirable chemical andphysical characteristics until just before use. Storage temperature inthe liquid supply vessel can be maintained readily by an automaticallycontrolled heating or cooling system.

The air pressure at the sprayheads can be adjusted over a wide range bymeans of a control valve (not shown) which may be located in the airflow system, preferably in the system between the blower and the plenumchamber. Control of the rate of flow of etchant or other liquid going tothe sprayheads is also desirable to obtain optimum results with theequipment. Such a controlled supply of liquid may be obtained in manyways and through various mechanisms so only the desired characteristicsof the liquid feeding and metering unit will be here described Therewill be a suitable supply vessel or source for the liquid and the liquidwill pass therefrom through a feeding and metering device in the form ofa pump which will deliver the liquid at an even and controlled rateuniformly to all of the flexible tubes leading to the pairs of supplypipes 12 for the sprayheads 11. The liquid feeding and metering devicemust be such that the rate of flow can be set and maintained at anydesired level.

Although a particular fluid metering device is not herein described indetail, one that has been found eminently suitable for use with sprayingequipment according to this invention is being made the subject of apatent application Serial No. 376,749, filed concurrently herewith byOrin B. Johnston and entitled Fluid Metering Device.

After being atomized and sprayed, some of the excess spent etchant iscarreid by [the air flow to the discharge conduit 61. Most of the excessetchant falls by gravity into the sump and through drain pipe 62 can bedrawn 01f to -a container outside of the equipment. However, whentechnical requirements permit, the recovered etchant can be recycled.Although automatic recovery and recycling of the etchant is not hereshown, it is obvious that it can be provided for if desired.

In view of the fact that air pressure, air flow and temperature, etchantflow and temperature, carriage speed and sprayhead oscillatory frequencyand travel can be readily adjusted, a liquid spraying system accordingto this invention is ideally suited for complete automation.

The double chamber basic arrangement shown FIG. 3 may be incorporated inapparatus according to FIGS. 4 through 9 of the drawings by providingtwo adjacent spray chambers, one applying etchant to the workpiece andthe other providing a neutralizing liquid. As the carriage moves theworkpiece from the etchant chamber to the neutralizing chamber, anyresidual etching effect caused by etchant remaining on the part will bestopped rapidly. The neutralizing and etching. fluids can be chemicallybalanced to a low hydrogen ion value through appropriate metering and itis possible to control this balance automatically so that the two fluidscan be mixed and discharged into a sewer. A third, a fourth, or morechambers could be provided beyond the first two, for carrying outsuccessive spraying operations such as washing, drying, coating, etc.

As will be evident from the foregoing description, certain aspects ofthis invention are not limited to the particular details set forth, andit is contemplated that vari ous and other modifications andapplications of the invention will occur to those skilled in the art.Therefore, it is intended that the appended claims shall cover suchmodifications and applications as do not depart from the true spirit andscope of the invention.

What is claimed as new and is desired to be secured by Letters Patent ofthe United States is:

1. Equipment for pneumatic spraying of a liquid on workpieces comprisingan enclosing cabinet with a spraying chamber therein,

a sprayhead in said cabinet extending into said spraying chamber,

said sprayhead having means supplying thereto at a constant rate aliquid to be sprayed,

means supplying a propellent gas to said sprayhead at a constant rate toatomize and propel liquid therefrom into said spraying chamber in theform of a spray having a localized nonuniform spray pattern,

means reciprocating said sprayhead back and forth in a first directionnormal to the spray from said sprayhead, transverse of said sprayingchamber,

a holder supporting workpieces in said spraying chamber maintaining themat a fixed distance from said sprayhead in the direct path of liquidsprayed from said sprayhead,

said holder including means for moving said workpieces through saidspraying chamber at a uniform rate in a second transporting directionnormal to the spray from said sprayhead, transverse of said sprayingchamber and substantially at right angles to said first direction ofreciprocation concurrently with said reciprocation and means in saidspraying chamber for collecting gas and sprayed liquid from saidsprayhead passing beyond said workpieces,

the said means reciprocating said sprayhead and said means for movingsaid workpieces-in transporting direction concurrently being timed sothat the localized non-uniform spnay pattern reaching said workpieces iscancelled out and uniform distribution of the sprayed liquid is obtainedon the workpieces.

2. Equipment for pneumatic spraying of a liquid on workpieces comprisingan enclosing cabinet,

a wall in said cabinet dividing it into a plenum chamber and a sprayingchamber,

a plurality of spaced sprayheads in said cabinet, each extending fromsaid plenum chamber into said spraying chamber, each sprayhead havingmeans supplylng thereto a liquid to be sprayed,

means supplying air to said plenum chamber and from said plenum chamberto each sprayhead to atomize and propel liquid from each sprayhead intosaid spraying chamber in the form of a spray,

means reciprocating said sprayheads in unison back and forth in a firstdirection transverse of said spraying chamber,

means for supporting workpieces in said spraying chamber at a fixeddistance from said sprayheads in the direct path of liquid sprayed fromsaid heads, including means for moving said workpieces through saidspraying chamber in a second transverse direction at right angles tosaid first direction of reciprocation and means in said spraying chamberfor collecting air and sprayed liquid passing beyond said workpieces. 3.Equipment according to claim 2 oomprosing in addition a closed loop ductsystem connected to said spraying chamber and to said plenum chamber,said duct system receiving air from said means for collecting air andincluding means pumping such air under pressure from said sprayingchamber through said system and back to said plenum chamber so that airsupplied to atomize and propel liquid from the sprayheads is collectedand recirculated by the system for repeated use spraying.

4. Equipment according to claim 3 comprising in addition filtering meansin said duct system for removing entrained liquid from the air collectedin said spraying chamber so that air pumped back to said plenum chamberis free from such entrained liquid.

References Cited by the Examiner UNITED STATES PATENTS 2,305,811 12/1942Oeckl 134165 X 2,770,501 11/1956 Coanda 239429 2,815,298 12/1957 Heflley118323 X 3,121,037 2/1964 Bo-ites 156345 X 3,182,671 5/1965 Vorie134-102 X CHARLES A. WILLMUTH, Primary Examiner.

R. L. BLEUTGE, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,282,273 November 1, 1966 Orin B. Johnston et al It is hereby certifiedthat error appears in the above numbered patent requiring correction andthat the said Letters Patent should read as corrected below.

Column 2, line 61, for "is" read it same line 61, after "such" insertcase column 3, line 38, for "rereverse" read reverse line 39, for"reciprication" read reciprocation line 52, for "assemly" read assemblyline 65, for "encolsure" read enclosure line 69, for "bottim" readbottom line 71, for "scavening" read scavenging line 73, for "the side"read one side column 4, line 21, for "propellant" read propellent line30, for "propellant" read propellent column 6, line 15, strike out "is";line 26, strike out "rate from the chamber.

A chemically inert atmos-" and insert instead rates, a "vacuum" orsub-atmospheric pressure can line 27, for "creatted" read created column7, line 41, after "described" insert a period; line 57, for "carreid"read carried Signed and sealed this 5th day of September 1967.

(SEAL) Attest:

ERNEST We SWIDER EDWARD J, BRENNER Attesting Officer Commissioner ofPatents

1. EQUIPMENT FOR PNEUMATIC SPRAYING OF A LIQUID ON WORKPIECES COMPRISINGAN ENCLOSING CABINET WITH A SPRAYING CHAMBER THEREIN, A SPRAYHEAD INSAID CABINET EXTENDING INTO SAID SPRAYING CHAMBER, SAID SPRAYHEAD HAVINGMEANS SUPPLYING THERETO AT A CONSTANT RATE A LIQUID TO BE SPRAYED, MEANSSUPPLYING A PROPELLENT GAS TO SAID SPRAYHEAD AT A CONSTANT RATE TOATOMIZE AND PROPEL LIQUID THEREFROM INTO SAID SPRAYING CHAMBER IN THEFORM OF A SPRAY HAVING A LOCALIZED NONUNIFORM SPRAY PATTERN, MEANSRECIPROCATING SAID SPRAYHEAD BACK AND FORTH IN A FIRST DIRECTION NORMALTO THE SPRAY FROM SAID SPRAYHEAD, TRANSVERSE OF SAID SPRAYING CHAMBER, AHOLDER SUPPORTING WORKPIECES IN SAID SPRAYING CHAMBER MAINTAINING THEMAT A FIXED DISTANCE FROM SAID SPRAYHEAD IN THE DIRECT PATH OF LIQUIDSPRAYED FROM SAID SPRAYHEAD, SAID HOLDER INCLUDING MEANS FOR MOVING SAIDWORKPIECES THROUGH SAID SPRAYING CHAMBER AT A UNIFORM RATE IN A SECONDTRANSPORTING DIRECTION NORMAL TO THE SPRAY FROM SAID SPRAYHEAD,TRANSVERSE OF SAID SPRAYING CHAMBER AND SUBSTANTIALLY AT RIGHT ANGLES TOSAID FIRST DIRECTION OF RECIPROCATION CONCURRENTLY WITH SAIDRECIPROCATION AND MEANS IN SAID SPRAYING CHAMBER FOR COLLECTING GAS ANDSPRAYED LIQUID FROM SAID SPRAYHEAD PASSING BEYOND SAID WORKPIECES, THESAID MEANS RECIPROCATING SAID SPRAYHEAD AND SAID MEANS FOR MOVING SAIDWORKPIECES IN TRANSPORTING DIRECTION CONCURRENTLY BEING TIMED SO THATTHE LOCALIZED NON-UNIFORM SPRAY PATTERN REACHING SAID WORKPIECES ISCANCELLED OUT AND UNIFORM DISTRIBUTION OF THE SPRAYED LIQUID IS OBTAINEDON THE WORKPIECES.